weather, and how it works

8/11/2019 Weather, And How It Works

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Earths Journey Through Space

Electromagnetism, and How It Works

Gravity, and How It Works

Great Extinctions of the Past

Great Inventions of the 20th Century

Great Moments in Space Exploration

Volcanic Eruptions, Earthquakes, and Tsunamis

Weather, and How It Works


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By Randi Mehling


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Scientific American: Weather, and How It Works

2007 by Infobase Publishing

Scientific American is a registered trademark of Scientific American, Inc.

Its use is pursuant to a license with Scientific American, Inc.

All rights reserved. No part of this book may be reproduced or utilized in

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photocopying, recording, or by any information storage or retrieval systems,

without permission in writing from the publisher. For information contact:

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ISBN-10: 0-7910-9053-1

ISBN-13: 978-0-7910-9053-4

Library of Congress Cataloging-in-Publication Data

Mehling, Randi.

Weather, and how it works / Randi Mehling.

p. cm. (Scientific American)

Includes bibliographical references and index.

ISBN 0-7910-9053-1

1. WeatherJuvenile literature. I. Title. II. Series: Scientific American

(Chelsea House Publishers)

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CHAPTER ONEWeather: You Like It or Not 7

CHAPTER TWO

The Air We Breathe 16

CHAPTER THREE

A Hot World Under Pressure 23

CHAPTER FOUR

Its All About Water 32

CHAPTER FIVE

Windy,Wild Weather 42

CHAPTER SIX

How to Forecast the Weather 51

CHAPTER SEVEN

Is Our Climate Changing? 59

Glossary 66

Bibliography 68

Further Exploration 69Index 70

About the Author 72

Picture Credits 72

Contents


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I I I I I I I I


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Weather:You Like It or Not

Weather:You Like It or Not

Weather: You Like It or Not 7

cross the flat prairies of Kansas, lightning strikes the

ground with a zigzag bolt of electricity. A few seconds

later, thunder booms. Hailstones fall from the sky, cooling off

this hot, humid summer day in mid-August. Some are as big as

golf balls and dent cars upon impact.In the Florida Keys, it is hurricane season, and an 85-mile-per-

hour (137-kilometer) wind tears off roofs, floods streets, and

knocks down telephone poles.

In January, a blinding blizzard in northern Michigan forces all

transportation to a halt, dumping three feet of snow in some

places. Winds pile up snowdrifts that cover most parked cars.

Meanwhile, in the Southern Hemisphere, January is summer-

time in Australia, and it is a sunny Saturday in the upper eight-

ies. Thousands of people have flocked to the beach to enjoy the

beautiful weather.

What do all these scenes have in common? They describe the

weather. Since the earliest of humankinds days on the planet, we

have tried to make sense of the outdoor conditions of rain, sun,

sleet, hail, wind, and snow. It seems as if the world goes crazy

during hurricanes, tornados, and thunderous storms. There isno escaping the weatherit affects every aspect of our lives.

CHAPTER ONE

A

I


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Hurricane winds have been known to rip coconuts off palm trees and sendthem flying through the air at high speeds. Thats another reason to stayinside during a hurricane!

Every living creature on Earth depends upon the weather for

its survival. Farmers depend upon rain to grow the food we eat.

Schools close when it snows a lot, and planes cannot depart

with ice on their wings. Without water from rain and snow, life

would not exist on the planet. Sailboats use wind to travel

around the world. We even choose which clothes to wear based

on the weather. It is no wonder the most common conversation

between two people, in any country and in any language, is

about the weather and what it might do next.

Weather happens, whether we want it to or not. It is com-

pletely uncontrollable and often takes us by surprise. Do you

know of anyone who can stand outside and tell a thunderstorm

to stop raining or redirect the wind to blow somewhere else?

Because it is so vital to our everyday life, people have always

tried to understand and predict the weather. By knowing theweather ahead of time, we can better prepare for it. We carry an

8 Weather, and How It Works


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Pinecones have traditionally been used to forecast the weather. Their

shape changes depending on the moisture in the air. They open up in

dry weather and close in damp weather. The petals of the morning

glory flower act in a similar way. It has been observed that the flower

shuts its petals before rain and bad weather and opens its petals for

fine weather. Scientific evidence has proved that these are indeed reli-

able and useful weather indicators.

If morning glory flowers open their petals, it will most likely be a

sunny day.


umbrella when rain is forecast. We postpone a trip if a major

storm is brewing. Farmers might plant extra rows of crops in

anticipation of a wet growing season. Sailors might travel a dif-

ferent route to avoid a storm or to take advantage of strong sail-

ing winds.

Nature Forecasts the Weather

The first humans did not have thermometers, weather satellites,

The Weather Channel, or the Internet. Instead, the first weather

forecaster on the planet was nature. People observed the world

CAN PINECONES PREDICT THE WEATHER?


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around them and noticed that nature provided many clues

about the weather. Plants and animals behaved differently

before certain weather events and so informed us of what type

of weather to expect. People predicted the weather based on

these signs from nature but never with 100% accuracy. Howev-er, these natural patterns occurred often enough for people to

believe in them.

Passed along from generation to generation, these signs of

weather eventually become known as weather folklorewell-

known sayings that people use all the time to forecast the

weather. There are literally hundreds of these weather predic-

tions based on nature. Weather folklore relies on patterns ob-served over a long time, not scientific measurement. However, it

is very interesting to note that scientific methods have proved

that many of these natural forecasts are true.

The weather is about as easy to predict as giving your cat a

bubble bath. Even today, with high-tech science, we cannot pre-

dict the weather with complete accuracy. Many people all over

the world choose to combine modern scientific technology withthe signs that nature provides to give them the best possible

weather forecast.

Ancient Ideas About Weather

Archaeologists, who study ancient civilizations, tell us that the

people from those timesmore than 4,000 or 5,000 years ago

believed gods were responsible for the whims of weather. A dif-

ferent god was in control of a particular aspect of the weather,

such as rain, wind, or thunder. Weather does seem magical. It is

always changing, and we know it is uncontrollable. Weather

helps us sometimes, and other times it causes us tremendous

harm. For instance, rain helps to nourish fruits, vegetables, and

grains. It provides us with water to drink. Yet, other times rain

has the power to devastate. It can be accompanied by lightning,

which can strike and kill a person. Rain can cause flashfloods,which can wash out an entire town.



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Many indigenous people in the United States and throughout the worldperform rain ceremonies. In these ceremonies, people of all ages participatein songs, dances, rituals, and prayers, just as their ancestors did hundreds oreven thousands of years ago.

In order to explain these positive and negative experiences of

nature, ancient cultures and civilizations intertwined religion

with the weather. Most thought supreme beings (in the forms of

gods and goddesses) had the power of life and death over them

and lived in fear of offending the gods. An angry god might cre-

ate a long-lasting drought, causing crops to die. People and ani-

mals would go thirsty and hungry; many would die.

These civilizations created many rituals in which ceremonial

offerings were made to please the gods. Grains and jewelry were

offered, and it was common to sacrifice animals and even, some-

times, humans. In exchange for the peoples devotion to their

gods, it was believed that they would be rewarded with bounti-ful crops and prosperity.



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The thunderbird is a very important mythical figure in Native American

cultures. Living high in the mountains, the thunderbird flaps its wings,making the sky shake with thunder. When the thunderbird blinks or

looks down, lightning shoots out of its eyes and hits the ground.Tribes in

the Pacific Northwest have a thunderbird to protect them and often

carve its figure on the top of totem poles.

Animals, figures, and shapes are carved in a specific order on totempoles, which can be more than 40 feet (12 m) high.The designsshown on the totem pole above tell stories or legends about the

Indians who lived around Vancouver, Canada.

Gods of Thunder and Sky

The Incas worshipped many gods and goddesses. Each one was

connected to a type of weather. For instance, the Incas prayed to

their rain god Apu Illapu when they needed rain. They believed

he drew water from the Milky Way and then poured it down onEarth as rain. Even in modern times, there are still many Inca

descendants living in Peru who worship the original Inca gods.


THE THUNDERBIRD


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The ancient Maya believed gods controlled the natural ele-

ments of water, wind, fire, and earth. Chac is a benevolent Maya

rain god who, as the legend goes, had a frog orchestra (because

frogs are thought to be calling the rain when they croak). Today,

modern ancestors of the Maya, the people of Yucatn, Mexico,still refer to Chac when they want it to rain.

In Norse mythology, Thor is the god of thunder and sky. Leg-

end tells how he chased away the frost. The rolling wheels of

Thors chariot rumbled like thunder, and he hurled his mighty

hammer like a lightning bolt at the frost giants. Thor is cred-

ited with the return of warm spring rains to the land.

Revealing the Mystery Behind Weather

The Greek philosopher Aristotle wrote a book around 340 B.C.

calledMeteorologica. In it, he explained his ideas on such weather-

related topics as clouds, wind, lightning, snow, and climate

change from a philosophical, not a scientific, point of view.

Interestingly, Aristotles ideas on these natural forces and their

relationships to each other were thought to be true for about2,000 years.

Toward the end of the sixteenth century, scientific instru-

ments that could measure characteristics of the weather were

invented. Because of this new scientific data, the majority of

Aristotles ideas were disproved. However, some of Aristotles

conclusions were proved correct, perhaps showing us that the

best scientific tool is an observant, analytical mind. Today we

use the word meteorologyto describe the science of weather and

weather forecasting.

Several important achievements occurred during the scientific

revolution of the sixteenth and seventeenth centuries. These dis-

coveries shaped our knowledge of meteorology and continue to

help us understand the weather even today in the twenty-first cen-

tury. Italian architect Leon Battista Alberti invented the first

mechanical wind vane in 1450. This gave us the ability to tell thedirection of the wind. Galileo Galilei invented the thermometer



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Evangelista Torricelli built the first mercury barometer in 1644. Also known

as Torricellis Tube, this invention allowed scientists to measure the pressureof the atmosphere.

around 1593, allowing the measurement of temperatures. Evange-

lista Torricellis barometer was invented in 1643 and measured

the weight of airalso known as air pressure. Because of these

scientific inventions, we now know that changes in temperature

and air pressure create the wind that powers our weather.


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Instruments that measured meteorological data continued todevelop during the eighteenth and nineteenth centuries. Scien-

tists soon learned that different locations around the world

experienced different types of weather conditions. Yet a scientist

in Italy had to wait weeks or possibly months to get news of

weather in the United States. Even within the United States, it

took a long time to share this exciting weather information.

The widespread use of the telegraph by 1843 changed that. Nomatter where researchers were living, the weather happening

right then and there was recorded and transmitted to a central

location. The telegraph allowed scientists to create the first

weather maps of the entire world. For the first time, scientists

could track how the weather on one side of the world affected

weather around the globe.

Today, meteorological scientists know that weather is a mix-

ture of the air we breathe, the Suns energy, the rotation of

Earth, and the movement of water and wind. Technologies such

as Doppler radar and satellites assist meteorologists as they con-

tinue to unravel the deep mysteries of the weather.


Thomas Jefferson, the main author of the Declaration of Indepen-

dence and the third U.S. president, was also one of our nations first

weathermen. For more than 40 years, Jefferson maintained an almostunbroken record of weather observations. He did this wherever he

was in the United States as well as on visits to France. Today, more

than 11,000 volunteer weather observers send local weather informa-

tion to the National Weather Service as part of the Cooperative

Observer Program.

FOUNDING FATHER OR WEATHERMAN?


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The Air We BreatheThe Air We Breathe

ake a deep breath. The air you breathe makes up the weath-

er. The term weatherdescribes what the air is doing in anyparticular time and place. For instance, the air can be warm,

cold, wet, dry, calm, or windy, depending upon where you are in

the world.

The climate describes the typical weather of a geographic

area on Earth. For example, the climate in Antarctica is very

cold, whereas in the tropics, such as Tahiti, the climate is very

hot. We know these climates are typical because the weather

patterns there have not changed for a long, long time. Climate

can be very different, even if two regions are close in distance. It

could be snowing on top of a mountain, and in the valley below

it could be raining.

We feel the sensation of the air on our skin each day and

choose our clothes to either stay warm or cool. However, where

does air come from? We know we need oxygen to breathe, but

what else is air made of? Lets begin at the beginningthe birthof our planet.


CHAPTER TWO

I

T


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As viewed from space, a protective layer of atmosphere surrounds ourplanet Earth.

Its a Gas

About 4.5 billion years ago, the planets in the solar system

formed from the dust and gas that surrounded the Sun. The two

most abundant elements in the universe are helium and hydro-

gen. These gases cloaked the newly formed planets like a protec-

tive blanket. This is called an atmosphere. However, Earths

gravity was not strong enough to hold onto this new atmos-

phere, and these gases floated back into space. The other plan-

ets that orbited close to the SunVenus, Mars, and Mercury

could not retain their atmospheres either.

Then something amazing happened on Earth. Our planet cre-

ated its own atmosphere. At its center, Earth was extremely hot

and unstable. All over the world, gigantic volcanic eruptions

ripped through the surface of the planet, bringing elementsfrom its core to the surface. Water, carbon dioxide, methane, sul-



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This specially-photographed image shows pollution over New York City.Scientists have linked increases in childhood asthma to air pollution.



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fur, and nitrogen filled the empty space around Earth. This time

the atmosphere stayed put. Earths gravity was strong enough to

hold these gases to the planet.

Our air was born. There was just one thing missing: oxygen.

Nothing alive today would be able to breathe this toxic brew ofsteam, sulfurous clouds, and carbon dioxide. The whole world

probably smelled like a rotten egg (which releases sulfur).

Luckily, life did evolve under these circumstances. About one

billion years ago, plants began to photosynthesize. They released

oxygen into the atmosphere. Ozone (three oxygen atoms) formed

from oxygen gas (two oxygen atoms) and floated about 10 to 20

miles up in the sky. This ozone layer absorbed the intenseultraviolet (UV) rays from the Sun, protecting the plant life.

Plants flourished, and more oxygen went into the atmosphere

surrounding the planet. Eventually there was enough oxygen to

support oxygen-breathing animals such as dinosaurs and mam-

mals, including humans.

The Protective ShieldOur AtmosphereThe main ingredient in our air is nitrogen (about 78%). Oxygen

makes up the next biggest portion, forming about 21%. The

remaining 1% of our atmosphere contains trace amounts of other

gases, including carbon dioxide, hydrogen, argon, helium, neon,

krypton, xenon, and water vaporwater in its gaseous form.

These gases constantly mix and swirl together to form our air,

which sustains all life on Earth. The atmosphere is made up of


Tie a piece of string in the middle of a stick so that it balances when

you hold the string. Tie an empty balloon to each end of the stick. The

two balloons should balance evenly. Now, untie one balloon and blow

air into it. Tie the blown-up balloon back onto one end of the stick.

The end with the blown-up balloon should dip downward. The bal-

loon filled with air is heavier than the empty one.

TESTING THE WEIGHT OF AIR


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five layers, like blankets piled on top of each other. The blanket

closest to Earth is the heaviest and contains the most air. As you

move higher into the sky, the blankets get lighter and lighter.

This is because the higher you go, the less air there is.

The layers act like a protective shield. They maintain a com-fortable temperature on Earth. Without an atmosphere, we

would be burnt to a crisp by the powerful heat of the Sun dur-

ing the day or freeze to death during the cold night.

Ozone, carbon dioxide, and water make up only a tiny portion

of our air, less than 1%. However, they have very important jobs:


The Sun is the largest

object in the solar sys-

tem.

More than one million

Earths can fit inside the

Sun.

The Sun is approxi-mately 4.5 billion years

old and is roughly half

way through its life-

span, estimated at 10

billion years.

Scientists predict that

in about 4 to 5 billion

years, the Sun willbegin to run out of its

hydrogen fuel and swell

up to 100 times its

present size.

When the Sun expands,

scientists theorize that

the inner planets,

including Earth, will be

engulfed and destroyed.

SUNNY FACTS

Even though the Sun is 93 million miles(150 million km) from Earth, it powersour world with infrared light. This ener-gy is absorbed in the troposphere and

provides us with most of our heat.


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they all protect life on Earth. The ozone layer in our atmosphere

acts like a filter. It blocks the Suns harmful UV rays 20 miles (32

km) above our heads. Without the ozone layer to protect us, theUV rays would be too intense for life to survive. Carbon dioxide

provides food for plant photosynthesis. Water, with assistance

from the Sun, provides us with all the different types of weath-

er we have here on Earth, such as clouds, rain, and snow.

Layers of the Atmosphere

Remember that the layers of the atmosphere are held around theplanet by the force of gravity. The layer of air closest to the

ground is called the troposphere. It extends about 7 miles (11

km) up from the ground. All weather happens in this layer

because it contains most of the water vapor in the air. Most

clouds form in this layer.

In general, as you move higher into the sky, each layer of the

atmosphere gets progressively colder. This is because Earth

absorbs the heat from the Sun faster than the air does. It makes

sense that the troposphere is the warmest layer of the atmos-

phere. It is the layer closest to Earth. The higher you go in the

sky, or the greater your altitude, the colder it gets.

The second layer of air above Earths surface is the strato-

sphere, which extends from about 7 to 31 miles (1150 km) in

the sky. Ozone is found in the stratosphere. Because ozone

absorbs high-energy UV rays from the Sun, this layer is actuallywarmer than the troposphere. The presence of ozone creates a


Many universities and private research facilities contribute to the sci-

ence of meteorology. In 1949, for example, a meteorologist named

Duncan Blanchard worked for the General Electric Research Labor-atory in New York. He discovered how to photograph raindrops and

showed that they are not shaped like tears after all. In fact, small rain-

drops are round, and large ones are shaped like hamburger buns.

RAINDROP PHOTOGRAPHY


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special exception to the rule that it gets colder as you movehigher into the sky.

The mesosphere is the third layer of atmosphere above the

ground. The air here is very cold, and temperatures can average

100F (73C). The altitude of this layer is between about 31

and 50 miles (50 and 80 km) up in the sky. The higher you trav-

el, the less air there is. Scientists say the air thins as you travel

up toward space.

The fourth and fifth layers of the atmosphere are found at

very high altitudes. The thermosphere is about 50 miles (80 km)

above Earth. Astronauts and space shuttles travel in this layer of

the atmosphere. Once you are up beyond 300 miles (480 km),

you are in the fifth layer, the exosphere. Weather satellites are

located in this layer. The upper limit of Earths atmosphere is

about 6,200 miles (10,000 km) in the sky. At this point, there is

hardly any air left. What little air remains in the exosphere layerescapes Earths gravity and floats into space.


Clouds form in the troposphere, where airlines fly. A balloon floats above inthe stratosphere; meteor showers (lower center) occur in the mesosphere. Thespace shuttle and aurora lights are above in the thermosphere. Different kindsof electromagnetic radiation (left to right) penetrate the atmosphere: gammarays, X-rays, ultraviolet rays, a rainbow of visible light, and radiowaves.


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he gases that make up our air are constantly moving, mixing,

and churning in every direction, like soup simmering in a

pot. They get their energy from the Sun. Sunlight warms the tem-perature of the air above Earth and sets these gases in motion.

However, there is more to the story. Earth rotates every 24

hours on its axis. This spinning of the planet also contributes

greatly to the movement of air. The movements of air create all

the different types of weather we know, including wind, rain,

and sunny days. Lets explore how air moves.

Gravity Keeps Us Grounded

Gravity is the force that pulls everything toward the ground.

Humans, dogs, trees, buildings, clouds, and the gases in our

atmosphere are all held to the earth because of gravity. Without

this invisible hold on us, we would be weightless and drift above

the ground. The planet would have no atmosphere because the

gases would just drift out to space.

Gravity gives everything a certain weight. The weight of yourbody puts pressure on loose dirt and leaves a footprint. The


A Hot WorldUnder PressureA Hot World

Under Pressure

CHAPTER THREE

I

T


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more you weigh, the more you push on the ground and the

deeper the footprint you leave.

Air also presses down on Earths surface because it has a cer-

tain weight. Its weight is known as air pressure. Air pressure is

always changing. It weighs more in some geographic areas,called high-pressure regions, and less in other places, called

low-pressure regions. A barometer is one tool used to measure

the weight of air.

Air travels like water in a river. It naturally flows from areas

of high pressure to areas of low pressure. The difference

between high- and low-pressure areas is one of the main rea-

sons we have any weather at all. Still, how exactly does air putpressure on us?

The Highs and Lows of Pressure

Although we are not aware of it, the gases in our atmosphere are

made of trillions of molecules bouncing around, bumping and

pushing into each other. For example, oxygen is a molecule.

Nitrogen is a molecule. Carbon dioxide is a molecule. These airmolecules are constantly moving up, down, sideways, and diag-

onallylike ping-pong balls in a clothes dryer.

If you were an air molecule, you might feel like you were

being pelted with snowballs your whole life. Each time another

molecule crashed into you, you would feel its impact on your

body. Scientists gauge the pressure of air by measuring the num-

ber of these impacts.

Take the balloon that was full of air from the experiment you did in

Chapter Two. When you filled the balloon with air, the increasing air

pressure expanded the sides of the balloon. The air pressure inside it

is high. Now, untie the balloon, and let the air out. What happens? The

air immediately flows from inside the balloon to outside the balloon,

where the air pressure is lower.

TESTING AIR FLOW


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Wind turbines harness the power of the wind instead of fossil fuels to gen-erate electricity. A wind farm is a bunch of wind turbines in one location.



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A barometer measures changes in atmospheric pressure and is used toforecast the weather.

The more air there is, the more air weighs, just as the more of

you there is, the more you weigh. The more air weighs, the more

impacts there are. This all means higher air pressure. Less air

means there will be less frequent impacts. Therefore, the air

pressure is lower since the air weighs less. Air pressure is theweight of all the air molecules pushing down on the ground.

Let us now see how we can personally tell how much air

weighs, without using any scientific instruments or training.

The Weight of the World

The weight of air is the heaviest at the surface of our planet

because most of our air is located there. Scientists measure theweight of air on the surface at 14.7 pounds (6.7 kg) per square


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Mount Everest rises more than 29,000 feet (8,849 m) above sea level. Thefarther away you are from sea level, the less air there is. At the top there isonly one third of the amount of oxygen found at its base, so most climbersneed an extra supply of oxygen to reach the summit.

inch. This means that the amount of air molecules pressing

down on one square inch weighs 14.7 pounds. It is like an invis-

ible hand pressing down on everything and everyone.

You dont notice this pressure until you move to a higher alti-

tude. Air pressure becomes lighter and lighter the higher you go

because air thinsthere are fewer air moleculesas the altitude

increases. If you hike up to the top of a mountain, there is less

air there than on the ground. This includes oxygen, a major part

of air. So, the higher you climb, the harder it is to breathe.

At 18,000 feet (5,486 m) above the ground, there is much lessair pushing down. Because there is less air pushing down, there



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In 1714, Gabriel Daniel

Fahrenheit improved uponGalileos earlier design (a

water thermometer) by

constructing a mercury

thermometer. The Fahren-

heit scale was the first reli-

able way of measuring

temperature.Water freezes

just below 32 degreesFahrenheit, it melts just

above 32 degrees, and it

boils at 212 degrees. Here

in the United States,we still

measure temperature in

degrees Fahrenheit. How-

ever, the worldwide scien-

tific community uses the

Celsius scale to measuretemperature.

In 1742, the Swedish

astronomer Anders Cel-

sius proposed a new scale

for thermometers. Anoth-

er scientist named Jean-

Pierre Christin made addi-

tional improvements tothe Celsius scale in 1743. Water freezes at 0 degrees Celsius, and it

boils at 100 degrees Celsius.

CONVERSION OF FAHRENHEIT AND CELSIUS

To convert from F (degrees Fahrenheit) to C (degrees Celsius): Take

the temperature in Fahrenheit, and subtract 32 from it.Then, multiply

that number by 5 and divide it by 9.

To convert from C to F: Take the temperature in Celsius and multi-

ply it by 9.Then, divide that number by 5 and add 32 to it.

In 1742, Anders Celsius was creditedwith inventing the Celsius temperaturescale, which measures the freezingpoint of water at 0 and its boilingpoint at 100. On the Fahrenheit tem-perature scale, water freezes at 32 andboils at 212.

MR. FAHRENHEIT AND MR. CELSIUS


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is less weight, or air pressure, as well. The air at this altitude ismeasured at 7.3 pounds (3.3 kg) per square inch. That is almost

half the weight of air measured at the surface! At this altitude,

about half of all our atmospheres air molecules are below you

and about half are above you. Mountain climbers can feel light-

headed, dizzy, and nauseous at these high altitudes. They often

wear masks connected to oxygen tanks to help them breathe.

This allows them to avoid the symptoms of what is known as alti-

tude sickness.

As you fly up through the five layers of the atmosphere, the

air pressure eventually becomes zero. There is no longer any air

left to exert any downward pressure.

The Sun Moves the Air

How air moves is a whole other story. Weather is created by

changes in air pressure and temperature. The temperature getsthe whole process started.

Earth takes 36514 daysone yearto orbit the Sun. Because Earth is tiltedduring its orbit, each area receives different amounts of the Suns energy atdifferent times of the year. This is why we have seasons.


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The Suns rays go through the atmosphere and hit Earths sur-

face. This energy heats the land and the oceans. As the surface

warms up, heat rises and warms the air right above the surface. The

hotter the air gets, the faster the molecules bounce around. The

faster the warming air moves, the more its air pressure increases.As the air along the ground warms from the Sun, the air above

it remains cool. This cooler air also moves more slowly than

warm air. Because the cold air is found higher in the sky than

warm air, and because it moves more slowly than warm air, cool-

er air has a lower air pressure than warmer air.

Since air flows from high to low pressure, the warm air rises

toward the cold air. Warm air is lighter than cold air. Like a bal-loon, it rises higher and higher. Warm air gets colder as it rises.

At the same time, cold air sinks because it is heavier than

warm air. As it sinks closer to the ground, the cold air begins to

warm up. Directly above the ground the cold air is now com-

pletely warmed by the heat of Earths surface. It begins to rise

toward the cooler air. The air continues to trade places in an

endless cycle of circulation around the whole world.

Balancing Act

Yet, Earth does not heat up evenly. Some areas of the world, like

the tropics (near the equator), are much hotter all year round

than, say, the extremely cold areas near the North and South

Earths position in relation to the Sun is always changing.The planet

spins around its axis, an imaginary line that runs between the North

and South Poles. One complete spin takes 24 hours. This is why half

of Earth is lit and warm (daytime),while the other half faces away from

the Sun (nighttime). At the North Pole the Sun doesnt set at all in the

weeks surrounding June 21 (the Summer Solstice), whereas the South

Pole lies in continual darkness. The reverse is true in the weeks sur-

rounding the Winter Solstice (December 21).

NIGHT AND DAY


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poles. Because Earth rotates, the warm air and the cold air are

stirred up. This continuous movement of warm and cold air is

like a giant fan. It transfers heat from hot areas of the world to

cold areas. This worldwide air circulation helps Earth keep its

temperature in balance.However, there are vast temperature differences between the

equator and the North and South poles. Air circulation cannot

balance these extreme temperatures. It never completely cools

down in the tropics, and the poles never warm up. Therefore,

the tropics always have a surplus of heat, and the poles always

have a surplus of cold.

These temperature differences between the equator and theNorth and South poles are the reason we have weather. They are

the reason the air in the atmosphere will always be flowing from

high to low pressure. The hot air over the equator rises toward

the poles, replacing the cooler polar air. This cooler air sinks

toward the ground, flowing toward the equator. In doing so,

these air movementsalso known as windshelp create the

worlds weather.



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loods, thunderstorms, clouds, rivers, lakes, swimming pools,

snowballs, puddles, baths, ice cubes, and hot tea. What do

they all have in common? Water.

Water takes up less than 1% of the atmosphere. Yet, without

water, nothing could live on the planet. If water did not exist,there would be no swimming, fishing, or snowboarding. Plus,

regular bathing would be difficult.

The Water Cycle

Oceans, lakes, rivers, and streams cover about 70% of Earth. The

amount of water on Earth is finitethe amount never changes.

However, the amount of water on Earth is always being recycled

and changing what it looks like. Water can take on three different

forms, depending on how hot or cold it is. When the temperature

is above 32F (0C), water is a liquid. When it is colder than 32F,

water becomes block ice. When you boil liquid water, it becomes

a gas called water vapor. This is also called steam.

As it changes through each of its three forms, water moves up

into the sky and back down to the ground in a never-ending

cycle called the water cycle. It is also known as the hydrologiccycle.Hydro means water.

It's All About WaterIt's All About Water

CHAPTER FOUR

I

F


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Water is redistributed in a continuous cycle: evaporating from the oceanand the land and falling as precipitation; and flowing from the land to theocean in rivers and streams.

Evaporation and Condensation

It takes a lot of energy to constantly change from a gas to a liq-

uid to a solid. Sunshine provides this energy. The Suns rays heat

the oceans, lakes, and other bodies of water on the surface. As the

water heats up, the liquid water becomes warm water vapor and

forms part of the air. This process is called evaporation. We

know how warm air movesit rises into the sky. The amount of

water vapor in the air is called humidity. Without knowing it, we

are surrounded by water all the time in the air we breathe.

As the warm air rises, it begins to cool off the higher it goes.

As the air becomes colder, the water vapor changes into drops ofliquid. When lots of these drops accumulate, they form clouds,


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Have you ever had to scrape frost off the windshield of a car? Frost

forms when water vapor freezes into icy crystals on cold surfaces

such as windows and trees. Dew is water vapor that condenses into

drops of moisture during the cool night. You can see these dew drops

on leaves, plants, and spider webs.

As the temperature drops, the moisture in the air condenses intodew. When the temperature reaches 32F (0C) this dew freezes

into what we call frost.

mist, and fog. This is called condensation. Clouds are made

up of billions of tiny water droplets. If it is cold enough, the

water vapor condenses into ice. Clouds can also be made of ice

crystals along with water droplets. Fog and mist are clouds that

form near the ground instead of in the sky.Water droplets can only condense when there is dust, smoke,

or other tiny particles in the air. These particles are called con-

densation nuclei. They give the water vapor something to cling

to in order to become a droplet. When there is a lot of pollution,

DO YOU KNOW ABOUT FROST?


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Sunlight looks white, but its

really made up of different

colors: red, orange, yellow,

green, blue, indigo, and vio-

let. The colors of a rainbow

are always in the same or-

der.The Sun makes rainbows

when white sunlight passes

through raindrops. To see a

rainbow, the Sun must be

shining behind you as youlook toward the falling rain.

A popular way to remem-ber the order of the colorsof the rainbow is: ROY G.

BIV. The letters stand forred, orange, yellow, green,blue, indigo, and violet.

there are more particles in the air, and therefore more clouds are

able to form.

Water from the Sky

Without clouds, it would not rain. The tiny water droplets keep

condensing, and they grow larger and larger within the clouds.

When the water droplets are big enough, the clouds cannot con-

tain them. They fall to the ground as rain, snow, or ice, depend-

ing on the temperature of the air below the clouds. Any type of

water that falls from the sky is called precipitation. Preci-

pitation is usually absorbed into the ground or falls into riversand oceans.

COLORFUL RAINBOWS


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Each snowflakeis made of twoto about twohundred sepa-

rate crystals.

As the Sun heats the surface waters of the planet, water evap-

orates. This process of evaporationand the water cyclecon-

tinues indefinitely.

Rain and Snow

The two most common types of precipitation are rain and snow.

Rain can fall fast and furiously or light and gently. A drizzle is

made of very fine raindrops. Sometimes streets flood and river-

banks overflow when heavy rainstorms dump large amounts of

water on the ground in a short time. The monsoon season in

Asia is famous for this. Countries like India are soaked by rains for

six months of the year and are dry for the rest of the time. The

people of this country are used to this weather pattern.

Snow is ice that falls from the sky. A snowflake forms when

water vapor turns directly from a gas into ice without going

through the liquid stage. This means the air in the cloud is

below freezing. The tiny ice crystals stick together, just like a

water droplet, until they are heavy enough to drop out of the

cloud. However, as the snow falls through the air toward theground, the air might be warmer than it was in the cloud. Then,


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the snow turns to rain before it hits the ground. If the air stays

close to freezing, the snowflakes will not melt. It is common to

see snow on top of a mountain, where the air is colder, while it

is raining in the warmer valley below.

Hail and Sleet

When strong winds toss raindrops high inside clouds, they

freeze into balls of ice called hail. These chunks of ice are flung

up and down inside the cloud. Layers of ice build up and form

a rounded hailstone. The largest hailstone on record in the Unit-

ed States had a diameter of 7 inches (18 cm) and weighed one

pound (.5 kg). It was about the size of a cantaloupe melon andsped more than 100 miles (161 km) per hour as it fell from the

sky. The heaviest hailstone in the United States was about 5.5

inches (14 cm) in diameter and weighed 1.67 pounds (.76 kg).

The heaviest hailstone ever reported was in India and weighed

2.2 pounds (1.0 kg). Hail can be dangerous and cause crop and

even building damage. Hailstones look like stones and feel like

stones if they hit you on the head!Sleet is falling ice that is smaller and wetter than hailstones. It

feels like slushwater that is half liquid and half ice.

Clouds

Clouds can tell what the days weather holds in store for you,

based on their shape and size. There are three main types of

clouds floating in the sky: cirrus, cumulus, and stratus.

Snow takes up about 10 times the space as rain. Because it takes up

so much space, snow piles up quickly on the ground. You can test this:

Collect some snow in a glass and mark its level. After it melts, mark

the level of water in the glass. (By the way, it takes about one million

cloud droplets to provide enough water for one raindrop.)

SNOW AND RAIN ARE NOT THE SAME


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Cumulus clouds are puffy andusually mean fair weather.They have flat bottoms andhang low in the sky.

Cirrus clouds are thin, feathery, white,and wispy. Because they form high in thesky where it is very cold, they are madeof ice crystals, not water droplets.

Cirrus clouds look feathery and wispy, and cirrus literallymeans curl in Latin. They form high in the sky where it is very

cold, at around 18,000 to 40,000 feet (5,48612,192 m). Because

of this, they are made of ice crystals, not water droplets. The

wind is responsible for blowing cirrus clouds into curls. These

clouds are often called mares tails because they look like the

tail of a horse. Cirrus clouds often signal bad weather.

Those puffy clouds that look like cotton balls or cauliflower

floating in the sky are called cumulus clouds. They form much

lowerapproximately 2,000 to 6,000 feet (6101,829 m) above

the ground. Cumulus clouds are made of tiny water droplets and

are usually seen in fine weather against a blue sky.

If you see a wide sheet of gray, shapeless clouds very close to

the ground, it is probably a stratus cloud. These clouds stretch in

all directions and are often dark and gloomy. Light, misty rain

and drizzle typically fall from stratus clouds. Fog is a type of stra-tus cloud.


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Harmless cumulus clouds can quickly develop into large towering cumulo-nimbus clouds, which are associated with powerful thunderstorms.

Clouds also determine how hot or cold you feel. Clouds act as

insulators. They prevent the flow of heat, so a hot day will feel

even hotter if its cloudy. A cloudy nighttime sky will also hold

the heat of the day closer to the ground, so that the evening

feels warmer. Conversely, a nighttime sky without any cloudswill generally feel very chilly. There is nothing to keep the heat

close to Earths surface during the cold, sunless night.

Rain Clouds Predict Stormy Weather

Dont be fooled by sweet, fluffy cumulus clouds. Sometimes the

sight of these clouds tells us the weather will be nice. Under cer-

tain weather conditions, though, cumulus clouds will grouptogether and become rain clouds called cumulonimbus clouds.

Nimbus means rainstorm in Latin.

Cumulonimbus clouds are distinctively larger and darker than

cumulus clouds. They look gray or black. This is because they are


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so full of water and ice crystals that sunlight cannot shine

through them. They have the same puffy characteristics as

cumulus clouds. However, cumulonimbus clouds build higher

and more vertically into the sky-like towers. They often have flat

tops, like a blacksmiths anvil. Some of these clouds measuremore than 9 miles high (14 km)taller than Mount Everest.

Cumulonimbus clouds usually bring rain, hail, and thunder

with them. When you see these clouds, you can be sure of the

weather forecast. They can become so large and powerful that they

can dump as much as 3 feet (almost 1 m) of rain in one afternoon.

Thunderstorms and Forks of LightningWhen you notice a cumulus cloud change from a round shape

to a rising tower, be warned. A thunderstorm is likely on its

way. Thunderstorms often occur at the end of hot, sticky sum-

mer days. This is because the warm, moist air rises very quickly

to form large cumulonimbus clouds. It is very windy inside

these tall clouds. The water and ice in a cumulonimbus cloud

bang against each other, and electricity builds up. Eventually thecloud releases this electricity as a flash of lightning.

Lightning always takes the quickest route to the ground, usu-

ally striking the tallest object around, such as a tree or building.

This is why it is important to get to lower ground if you are hik-

ing on a mountaintop. You do not want to be the tallest object

around in a thunderstorm, and you do not want to be standing

nearthe tallest tree either!

Count the number of seconds between seeing a flash of lightning and

hearing the thunder. For every 5 seconds you count, the storm is about

1 mile (1.6 km) away from you. If the thunderstorm is close, the thun-

der will sound like a loud crack. A low, rumbling thunder means the

storm is farther away.The closer the storm, the faster you should seek

shelter from it!

HOW FAR AWAY IS THAT THUNDERSTORM?


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Thunder and light-ning actually happenat the same time.However, since light

travels much fasterthan sound, we seelightning before wehear thunder.

As lightning strikes the ground, it heats the air around it. This

has been measured at around five times the heat of the Sun,

about 55,000F (30,538C). When the air gets this hot, it sounds

like an explosion. The sound is called thunder. Thunder and

lightning happen at the same time, but we see lightning before

we hear thunder. This is because light travels at a much faster

speed than sound.

When lightning hits the ground, it is called fork lightning.

Lightning actually has two bolts. First, it zigzags to the ground

from the cloud. A split second later, the lightning races up the

exact route back to the cloud. Sheet lightning is lightning thatflashes within the cloud itself.


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Windy, Wild Weather

ind is air on the move, and it often creates dramatic

weather. It can flutter your hair in a summer breeze or

slap you across the face as a blizzard blinds you with snow or

a hurricane rips the roof off your house. Strong winds can bescary and dangerous, but they can be exciting as well. For exam-

ple, in 1999, scientists managed to put a Doppler radar inside an

Oklahoma tornado and measured the fastest recorded wind

speed of 318 miles (198 km) per hour.

Wind is described by its direction and speed. This allows mete-

orologists to track how fast and where a storm might hit in your

area. The three main forces that affect wind are high and low air

pressure, friction, and the rotation of our planet.

Pressuring Wind to Blow

Remember that Earth is heated unevenly. Warm, high-pressure

air near the equator is always rising, and cold, low-pressure air

from the North and South poles is always sinking. All air moves

from areas of high pressure to areas of low pressure. This move-

ment of air is the wind. A popular phrase to help you rememberthis is Winds blow from high to low.

Windy, Wild Weather

CHAPTER FIVE

I

W


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Windy, Wild Weather 43

Friction

Compared to the ocean, the land is an obstacle course for wind.

As the wind blows over land, it has to go over or around moun-

tains, buildings, trees, and cars. These obstacles actually rub

against the wind, causing friction. The force of friction eitherblocks or slows down the wind. You can notice this force when

using your feet to slow down your speed on a bike. The friction

between your feet and the roads surface is what slows your bike

down. Over the ocean, there is only flat water, no obstacles.

Winds over the oceans are much faster because of this, which is

why high-speed winds like hurricanes begin over the oceans.

Coriolis Effect

Every 24 hours, Earth rotates on its axis. Half of the planet is

heated every 12 hours, while the other half is in darkness. This

is one of the main reasons Earth is heated unevenly. These dif-

ferences in temperature create changes in air pressure that pro-

duce wind.

However, the winds do not blow in simple straight lines fromhigh to low pressure, flowing up and down the globe. Instead,

winds curve because our planet spins. This is called the Corio-

lis Effect. It bends every wind on Earth. Anywhere north of the

equator, called the Northern Hemisphere, the winds blow to the

right. Winds blow to the left anywhere south of the equator in

the Southern Hemisphere.

A batter in the major leagues has to watch the signs from the third-

base coach. He also must be aware of wind conditions. If a batter has

a 10-mile-per-hour (16-km) wind at his back, it will add about 30 extra

feet (9 m) to a long fly ball. However, if that same wind is blowing in

at the batter, it will shorten a fly ball by about 30 feet. Thats enough

of a difference to turn a home run into an out!

WIND MAKES A HOME RUN


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The strong winds from a hurricane cause ocean waters to rise many feetand then crash onto land in a powerful storm surge. A storm surge is oftenthe most dangerous part of a hurricane because it creates massive floodingin low-lying areas. This cyclist is taking a huge risk by playing in the surf after

a hurricane.

Naming Winds

The direction of the wind is based on the direction from which

the wind is blowing. Easterly winds blow east to west. Westerly

winds blow west to east.

We can depend upon particular wind patterns to stay the same

in certain places of the world. Sailors and sea captains count on

these winds remaining constant. For example, there are steady

winds known as trade winds, named during the early days of

sailing. Ships that traded goods between different countries

knew they could get to their destination quicker when their sails

caught hold of these winds. Another unique wind pattern is the

doldrums. Sailors avoid this area north of the equator between

the two trade winds because the winds there are often very lightand calm. They can trap ships in one spot for weeks.


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Sensing the Wind

There are ways you can accurately measure the direction and

speed of the wind by using simple technology and your own five

senses. For example, at airports, shipping ports, and seashores

wind socks can show the direction of the wind. Perhaps youhave seen thesethey are often a bright, day-glow orange. A

wind sock is tube shaped, with an open end and a closed end. It

is usually attached to a pole that is planted in an open area. The

wind blows into the open end of the sock, and it points the way

the wind is blowing. The wind sock also gives a general sense of

the speed of the wind. It flaps around gently in a light wind and

stands in a straight line in a strong wind.Another easy way to tell how fast the wind is blowing without

any scientific tools is with the Beaufort scale. This scale was orig-

inally developed in 1806 by Admiral Sir Francis Beaufort and is

still used today. By studying the effects of the wind on chimney

smoke, trees, and leaves, you can estimate the speed of the wind.

A chinook is a warm wind coming from the eastern slopes of the

Rocky Mountains. Chinooks occur most often in winter and can warm

temperatures more than 100 degrees in just a few hours. Typically, tem-

perature change is around 40 degrees. Temperatures rapidly cool once

a chinook leaves.

The Black Hills of South Dakota are home to the worlds fastestrecorded rise in temperature. After a chinook wind, the temperature

there rose from 4F (20C) to 45F (7C) in about 2 minutes. Sev-

eral hours later, the chinook was gone. It took only 27 minutes for the

temperatures to drop back down to 4F.

The record for rapid temperature change in the United States is

held by Great Falls, Montana, which on January 11, 1980, went from

32F (0C) to 15 F (9C), a 47-degree warm-up, in 7 minutes. That

was because of a chinook. Chinooks are called snow eaters because

of their ability to make snow melt rapidly.

CHINOOK WINDS


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The Birth of a Hurricane

During the day, land heats up quickly from the Suns energy. At

night, land also cools off quickly. The oceans are different. They

take a bit longer to warm up, but once they do, oceans tend to

stay warmer for a longer time than land does. This is the mainreason why we have hurricanes. They get their power from the

warm ocean water.

Hurricanes are tropical storms with very strong winds (over 74

miles or 119 km per hour). They form over the Atlantic Ocean

In August 2005, Hurricane Katrina struck the southern United States withwinds reaching over 155 miles per hour (249 km). However, it was the

storm surge from this powerful hurricane that devastated parts of Louisiana,Mississippi, and Alabama.


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in tropical areas near Central Africa. As the warm ocean heats

the air above it, high winds form. These high winds cause sea

water to quickly evaporate into the air. As a result, the air con-

tains a lot of warm water vapor, which rises into the air and con-

denses into clouds. This combination of heat and water creates

huge, ferocious thunderstorms. When several thunderstorms

clump together, the Coriolis Effect begins to spin them around

as one enormous weather system.

When winds reach between 39 and 73 miles per hour (63 and

117 km), this weather system is classified as a tropical storm and

is given a name. The high winds push this whole whirling thun-

derstorm across the ocean. It gathers more and more energy from

warm, moist air and grows larger. Like the spinning of a top, the

rotation of Earth twirls the storm faster and faster. Once the trop-ical storm reaches 74 miles per hour, a hurricane is born.

Hurricanes are given names to help identify and track them.Each hur-

ricane season, one name for each letter of the alphabet is selected

(except for Q, U,X,Y, and Z).The same lists are reused every six years.If a hurricane is very deadly or costly, its name is retired from the

list by the World Meteorological Organization, and a new name is cho-

sen. Well-known retired hurricane names include Hugo, Andrew, and

Charley.

The year 1953 marked the first season during which storms were

named using female names.The first official name went to Hurricane

Alice. Before this time, locals in the islands frequently referred to

storms by the name of the saint whose day was closest to the occur-rence of the storm. Storms were also often named after another cat-

astrophe.The Rising Sun Hurricane of 1700 recalls the sinking of the

Rising Sun and the 97 souls lost in the wreck. Hurricanes were also

named after places where they did greatest damage, such as the Galves-

ton Hurricane of 1900. Beginning in 1979, alternating male and female

names were assigned to new storms.

NAMING HURRICANES


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Rating a Hurricanes Intensity

The intensity of a hurricane is determined by its wind speed. The

Saffir-Simpson scale uses five categories to rate a hurricane. A Cat-

egory 1 is a mild hurricane and a Category 5 is the most severe.

Under the right conditions, hurricanes can last for a few weeks,often wreaking havoc on the East and Gulf coasts of the United

States and Mexico. Islands such as the Bahamas, Bermuda, and

the Virgin Islands often endure the effects of hurricanes.

Much of the hurricanes destruction affects people living

along the coasts. High winds create huge waves that swamp the

shoreline, washing away homes, cars, and even people. These

are called storm surges. Hurricane season begins June 1 and endsNovember 30. When a hurricane reaches cooler water or land, it

loses its source of energyheatand quickly loses intensity.

This satellite photo of Hurricane Rita clearly shows the eye of this Category

5 hurricane. Hurricane Rita hit Louisiana and Texas only a month after Hur-ricane Katrina blasted through.


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Strong winds are known by different names, depending on

where they form. Hurricanes form in the Atlantic Ocean,

typhoons in the Pacific Ocean, and cyclones in the Indian Ocean.

A Twisters Path

Tornadoes also form from cumulonimbus clouds, but over land

instead of water. Some of these clouds become so massive that

they create their own wind system within the cloud itself. A tor-

nado forms when the winds inside the storm cloud start to

rotate. This gives a tornado its telltale shapea tall, whirlingfunnel of air, also known as a twister. Tornadoes can be over 500

feet (152 m) wide.

Inside the funnel, air spins at enormous speeds, up to 250

miles (402 km) per hour. Tornadoes average 20 to 50 miles

(3080 km) per hour as they move along the ground. The fun-

nel acts like a giant vacuum cleaner that sucks up or destroys

everything in its path. Although tornadoes usually only last

about 15 minutes or less, they can travel several miles, destroy-

ing everything in their path. Because of their short lives, torna-

does are very hard to predict.

Tornadoes contain some of the fastest winds on Earth. They

are known for picking up all kinds of objects, such as cows, cars,

and tractor-trailers, before hurling them back to the ground.

Strangely, sometimes these objects are unharmed. There are sto-

ries of tornadoes plucking all the feathers from a chicken whileleaving the chicken alive.

The fastest wind speed ever recorded was 318 miles (512 km) per

hour. It was measured in a 1999 Oklahoma tornado. This tornado

broke the long-standing world wind record on top of Mount Washing-ton, the highest point in New Hampshire. A surface speed of 231 miles

(372 km) per hour was recorded there in 1934.

FASTEST WIND SPEEDS EVER RECORDED


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Midwestern states in the United States have the distinction of

having the highest number of destructive tornadoes in the

world. This stretch of land is known as Tornado Alley. States

such as Oklahoma, Kansas, and others in the Great Plains are

very flat. This allows cold, dry, polar air flowing down from

Canada to meet warm, moist, tropical air flowing up from the

Gulf of Mexico. Tornadoes form when these cold and warm airs

meet over Tornado Alley.

Twisters are so short-lived that they are very difficult to predict. Manyneighborhoods in Tornado Alley use sirens to warn of an approaching tor-nado, but this only gives people a few minutes warning, if that much!


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How to Forecastthe Weather

f you dont like the weather, wait five minutes. This pop-

ular saying reflects the lack of control we really have over

the weather. A basic understanding of the nature of clouds andwind can tell you what the weather will be like over the next few

hours. With weather satellites, Doppler radar, and other sophis-

ticated tools, todays meteorologists can predict the weather

several days in advance. However, there is no such thing as fore-

casting, or predicting, the weather with 100% accuracy.

A Meteorologists Work Is Never Done

There are many jobs for a meteorologist. You probably are most

familiar with meteorologists on television. Most meteorologists

work behind the scenes. For example, some work for the Tropi-

cal Prediction Center, part of the National Hurricane Center in

Florida, tracking tropical storms and hurricanes. These meteo-

rologists give people several days warning before a hurricane

hits land. This saves many lives.

Other meteorologists develop new technology to measure andunderstand the weather. They may work for the U.S. govern-

How to Forecastthe Weather

CHAPTER SIX

I

I



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ment weather organization, the National Oceanic and Atmos-

pheric Association (NOAA). The U.S.National Weather Ser-

vice is a branch of NOAA and has its main weather station in

Maryland. The NOAA has dozens of smaller stations all over the

country. These stations collect information about local climates,among other important tasks, so that meteorologists can see

long-term trends in the weather across the country.

However, without amateur meteorologists, the National

Weather Service would not be able to understand the weather as

efficiently as they do. Thousands of amateur observers across the

country love measuring and recording the weather. They volun-

teer as part of the NOAAs Cooperative Observer Program. Theseweather buffs provide valuable daily and monthly information

A wind sock tells you from which direction the wind is blowing. It also

gives you an idea of how strong the wind is. To make your own wind

sock, you will need:

sleeve from a big, old, long-sleeved shirt

wire

needle and thread

small rock or other weight

string or twine

1. Cut one sleeve off the long-sleeved shirt. Bend the wire into a circle

that is the same size as the top end of the sleeve (the end by theshoulder). Place the wire into this end of the sleeve, and attach it

with a few stitches.This is the mouth of the wind sock.

2. Place the rock or weight on one edge of the wire. Sew it on tight to

hold it in place. Tie the string onto the side of the wire opposite the

rock.

3. Tie the other end of the string to a branch where it can move freely.

The rock will keep the wind sock facing into the wind.

4. Now your wind sock is working. Use a compass to find out from

which direction the wind is blowing.

MONITORING THE WIND


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A storm chaser is a person who pursues severe thunderstorms. Chasers arepeople from all walks of life, most of whom are very knowledgeable aboutmeteorology. Contrary to Hollywood movies, chasers keep a safe distanceof a mile or more from tornadoes.

to the NOAA on such things as rainfall, snowfall, temperatures,and river levels. In times of threatening weather, amateur weath-

er observers have saved lives by quickly alerting the National

Weather Service about local conditions.

Tools of the Trade

No matter if they are professionals or amateurs, meteorologists

depend upon knowing the weather basics: temperature, air pres-

sure, rainfall, and wind speed and direction. The main difference

between meteorology in the 1800s and today is the level of

detail. The same basic information about weather is collected

and analyzed today as back then, but weather maps now allow

meteorologists to know in great detail what the weather is doing

and where it is doing it.

Technological inventions such as radar, satellites, and computers,

just for starters, enable meteorologists to probe ever more deeplyinto this global phenomenon we experience as the weather.



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The GOES-12 satellite shows Hurricane Rita swirling counter-clockwise inthe Gulf of Mexico, before making landfall on the coast.

The best weather forecaster studies global weather patterns

first, then focuses on to the entire United States, and finally looks

at the weather that is happening locally. Most storms begin

above 10,000 feet (3,048 m) and over an ocean. When a forecast-

er knows where a storm originates, she or he can track its course

and predict where the storm will go over the next few days.

Technology allows forecasters the see this big picture of

weather on a global and national scale. Doppler radar, radio-

sondes (instruments carried by weather balloons), satellites, and

computers are some of the advanced scientific instruments used

to collect this vital weather information across the entire planet.

Doppler Radar

RADAR is an acronym that stands for RAdio Detecting AndRanging. Early radar systems sent out powerful radio pulses that


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Since 1995, this Doppler on Wheels mobile radar system has allowedadventurous scientists to drive directly into tornadoes. Maps are created

from the Doppler images and have provided new insights into how torna-does form and evolve.

reflected off objects such as rain or clouds. The more rain or

clouds, the more they reflected the radar signal. This told mete-

orologists about the location and size of certain weather eventsbut not the speed and direction of the moving air.

Radar technology has developed quite a bit over the past 50

years. In the early 1990s, the NEXt Generation RADar system

(NEXRAD) replaced the older Doppler radar systems. Throughout


Meteorologists rely on hurricane hunters to learn more about hurri-

canes. Since 1944, these members of the Air Force Reserve have flown

planes equipped with weather instruments straight into the middle ofhurricanes.They immediately relay details about the hurricane to the

Tropical Prediction Center. One hunter described the experience as

being tossed about like a stick in a dogs mouth.

HURRICANE HUNTERS


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The nameTIROS standsfor TelevisionInfraRed

ObservationSatellites.These satellitesobserve Earthscloud coverand weatherpatterns fromspace.

the United States and overseas, there are about 159 NEXRADDoppler radar stations. Doppler radars gather weather data and

send it immediately to computers at the National Climatic Data

Center (NCDC), a division of the National Weather Service. A

map is generated that shows patterns of precipitation and its

movement anywhere in the world. Updates are provided every

five minutes. Doppler radar can show wind direction and speed

more than 500 miles (805 km) away. Doppler radar also detects

tornadoes before they form. Forecasters can now track storms days

in advance, making Doppler radar an invaluable tool. Advance

warnings of tornadoes and hurricanes have saved many lives.

Satellites

Satellites truly provide the biggest picture of Earths weather. In

1960, the TIROS 1 satellite sent meteorologists the first photos

of all Earths clouds. Until this point, meteorologists could onlysee sections of the worlds cloud cover. Since then, satellite tech-


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nology has rapidly advanced, providing nearly complete cover-

age of the worlds weather. Today, weather data from satellites is

never more than six hours old.

Like Doppler radar, U.S. satellites look for storms that can

threaten us. There are geostationary and polar-orbiting satellitesbeaming this information to weather stations all over the world.

The United States, Japan, and Europe have geostationary satel-

lites that orbit over the equator. They stay over the same spot

while Earth is spinning. To do this, they need to be stationed

about 22,000 miles (35,406 km) up to maintain just the right

speed to keep up with Earths rotation.

There are also two U.S. polar-orbiting satellites circling Earthfrom north to south, crossing over the South and North poles.

They fly only about 530 miles (853 km) up in the atmosphere.

Because Earth is rotating, these satellites capture images from


Twice a day, every dayof the year, weatherballoons are releasedsimultaneously fromalmost 900 locationsworldwide.The bal-loon flights last forabout two hours.Weather balloons candrift as far as 125miles (201 km) away

and rise up to morethan 20 miles (32 km)in the atmosphere.


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every part of the planet every 12 hours. Information from satel-

lites is channeled to a computer, along with information gath-

ered from other meteorological instruments.

RadiosondesRadiosondes are carried by weather balloons. Radiosondes allow

scientists to measure winds and greatly improve our understand-

ing of the weather.

Radiosondes that measure temperature, humidity, and pres-

sure are attached to large balloons and released thousands of feet

into the air. As the balloon rises higher in the sky, a radio trans-

mitter sends the weather data to radiosonde stations on theground. There are more than 900 radiosonde stations world-

wide. When the balloon bursts, the weather instruments (which

are wrapped together in a type of package) float to Earth on a

parachute. The National Weather Service releases hundreds of

radiosondes each day. About one-third of them are found, and

returned. If you find one, you just drop it in a mailbox, postage

free! Radiosondes were named for the word sonde, which is OldFrench for sounding line.

Computers

Whether it comes from an amateur weather observer, a barome-

ter, a satellite, or a weather balloon, every piece of weather infor-

mation is fed into supercomputers at the National Weather

Service. These supercomputers are able to compute more than 2

billion operations a second. Air pressure, Earths rotation, the

water cycle, and every other factor that completes the weather

puzzle are fed into these computers. Weather maps are created

that explain every weather action happening anywhere in the

world in that very instant.

This process is also called numerical forecasting. Numerical

forecasts allow weather forecasters to have an up-to-the-minute

knowledge of the current weather. This greatly enhances theirability to predict the weather with as much accuracy as possible.


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Is Our ClimateChanging?

ust as our weather always changes, the climate of Earth has

always changed as well. For example, ice ages blanketed

parts of Earth with thick ice on and off for thousands of years.

Volcanic eruptions have changed the climate in both directions.Molten lava can heat up a large area of the planet with its

intense volcanic energy. Volcanic ash spewed miles into the sky

can also block the Suns rays, causing the world to become cold

and uninhabitable. These cycles have been a part of Earths nat-

ural history since the birth of the planet billions of years ago.

Earth has always balanced its temperature by sending the heat

it receives from the Sun back out into space. However, certain

gases in our atmosphere trap the heat that is given off from

Earths surface. These are called greenhouse gases, since they

hold in heat like a greenhouse. Greenhouse gases, such as water

vapor, carbon dioxide, methane, and nitrous oxide, are an

important part of our atmosphere. They keep Earth from becom-

ing a ball of ice with surface temperatures of about 0F (18C).

Over the past century, many scientists have shown evidence

that these greenhouse gases are building up. This buildupincreases the amount of heat trapped close to the surface of

Is Our ClimateChanging?

CHAPTER SEVEN

I

J


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Air has no borders or immigration policy. We all breathe the same air.The pollution from a factory in the United States affects the air quality onthe other side of the world, and vice versa.

Earth. Therefore, Earth is warming up. Many scientists believe

human activities, including the burning of fossil fuels, are the

cause. These fuels, mostly gas and oil, release carbon dioxide

when they are burned. This is also called exhaust. The United

States produces about 25% of the worlds exhaust. Still, others

say the increasing world temperatures are just a natural part of

Earths normal cycle.

Evidence of Global Warming?

The Intergovernmental Panel on Climate Change (IPCC) is a

group of scientists from around the world who are brought

together by the United Nations. Every year, this group meets todiscuss recent scientific findings on climate change. They also


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Rising global temperatures are melting Earths polar ice caps and glaciers

and increasing the sea level. As global warming continues, millions of peopleare at risk from floods.

debate how a warmer climate could affect our modern societies.Rising sea levels, melting polar ice and mountain glaciers,

warmer oceans, and flooding are among the subjects of this sci-

entific research on climate change.

Smog is polluted fog. In cities such as Los Angeles, California, car

exhaust, forest fires, and industrial processes all release large particles

of pollution into the air. These particles are types of condensationnuclei that create clouds, or fog, near the ground. Smog is also known

as a combination of smoke and fog.The air pollution that creates smog

also makes it very difficult for some people to breathe. Studies show

that asthma rates in children are increasing.There is some evidence

that increased air pollution is the reason.

SMOG, POLLUTION, AND ASTHMA


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In addition to infrared

light, the Sun sends ultra-

violet (UV) light to Earth.

Most of it is blocked by

the ozone layer in thestratosphere. However,

certain man-made chem-

icals destroy this protec-

tive ozone layer, which

allows more UV light to

reach the planets sur-

face. Because UV light is

very harmful to livingcreatures and causes can-

cer, the use of these

ozone-layer-destroying

chemicals has been limit-

ed or banned since the

1980s. This has been a

worldwide success, and

today the hole in the

ozone is shrinking.

A satellite mapped the pink area outlinedin white as a severe depletion, or hole,in the ozone layer caused by pollution

over Antarctica.

Sheets of thick ice called glaciers form on some mountains in

various places of the world. These mountain glaciers have been

slowly melting over the past 100 years. This melting of glacial

ice has sharply increased over the past 30 years. The Arctic is also

covered with thick sheets of ice. Today that ice is 40% thinnerthan it was just 30 years ago. Many scientists point out that ris-

ing global temperatures are the reason for this melting.

Sea levels around the world rose 4 to 8 inches (1020 cm) dur-

ing the twentieth century. Some of this increase is partly from

the melting mountain glaciers. Many scientists believe that if

the temperature keeps increasing, even more glacial ice will

melt. One U.S. Environmental Protection Agency study foresees

THE HOLE IN THE OZONE


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A warmer climate brings more rain to some parts of the world and less toothers. The Amazon is now in its worst drought in 40 years.

a 1-foot (0.3-m) rise in sea levels on the Atlantic and Gulf coasts

by 2050 and a 2-foot (0.6-m) rise by 2100. A 2-foot rise in the

oceans would severely flood all coastal communities in the

world. This much ocean water would also permanently cover a

piece of the United States bigger than Massachusetts.

Evidence shows that ocean water is also heating up. Hurricanes

receive their power from warm water. Based on computer mod-

els, some scientists say as the oceans heat up, the destructive

strength of hurricanes will increase.

Scientists point out that it rains more now in certain areas of

the world than it did 100 years ago. As temperatures rise, we

could expect even more rainfall. Yet, scientists point out that

other parts of the world will experience more droughts. There

currently is not enough evidence to say whether drought isincreasing or not.


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A possible upside to global warmingis having warmer win-

ters. Although that means fewer snowball fights, it also means a

longer growing season. This translates into more food produc-

tion in certain areas of the world. There is already evidence in

Europe that the growing season is several days longer since the1960s. Spring plants now bloom about six days earlier.

It is important to remember that not all areas will have more

food. If the worlds temperatures keep increasing, those areas of

the world that are already hot and dry will not be able to grow

the same amount of food. Serious consequences will be felt in

places such as the tropics and parts of Africa. Scientists predict

that by the 2080s, about 80 million people, mostly withinAfrica, could go hungry because of climate change.

Humans Create Greenhouse Gases

Carbon dioxide gas is added to the atmosphere when fossil fuels

are burned, such as gasoline and oil. Human activities use enor-

mous amounts of these fuels. Each day, we use fossil fuels to

power all parts of our lives. For example, every time you drive ina car, you are using fossil fuels. One way to slow climate change

is to ride your bike more.

Carbon dioxide is removed from the air by plants during pho-

tosynthesis. When we cut down trees, we take away natures

ability to reduce carbon dioxide. Perhaps you can plant some

trees to help reduce this greenhouse gas in our air.

Cut out a square piece of white cloth. Next, cut out a smaller square

of cloth and glue it onto the middle of the first, larger square.Then,

hang it outside for about a week. Peel off the square in the middle. Is

the area underneath the smaller square cleaner than the surrounding

cloth? Whatever made the cloth dirty is in the air that you breathe.

Try placing the cloth in different locations, such as a park or near a fac-

tory. Notice if there are any differences.

HOW TO TEST AIR POLLUTION


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The worlds biggest contributors to greenhouse gas emissions, in particularthe United States and Russia, did not sign the Kyoto Protocol. Many con-cerned citizens protested against their own governments in the hopes ofchanging this decision.

Thousands of people all around the world are changing the

way they live in order to stop global warming. Most of theworlds governments have pledged to switch to cleaner fuels,

such as solar and wind energy. These do not release carbon diox-

ide into the air. Scientists are committed to researching new

technologies and processes that do not put more greenhouse

gases into our air.

The debate over global warming continues in scientific labs

and governmental offices. Whether climate change is human-

made or a natural cycle of Earths weather is still not complete-

ly understood. However, the evidence points out that the

worlds climate is shifting. The effects are visible. Perhaps we

should remember a most important thing: We all can make a

difference in our world.


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66 Glossary

air the mixture of gases that form the atmosphere of Earthair pollution chemicals or substances in the atmosphere that are directly or

indirectly harmful to living things

air pressure the weight of air pressing down on Earth. Air pressure can changefrom place to place, and this causes air to move, flowing from areas of high pres-sure toward areas of low pressure. It is the same as barometric pressure.

atmosphere the layer of gases surrounding a planet. Earths atmosphere isdivided into five layers: troposphere, stratosphere, mesosphere, thermosphere,and exosphere.

barometer an instrument that measures air pressureblizzard an intense winter storm where winds of 35 miles per hour or higher

blow falling snow.

weather, and how it works

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